1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming system, and an image forming method.
2. Description of Related Art
In order to reduce the burden on users when a jam (paper jam) occurs, a conventional image forming apparatus has an automatic purge function to automatically eject sheets remaining in the apparatus after a user removes only a sheet that has caused the jam. After all the remaining sheets are ejected, the image forming apparatus starts supplying sheets for recovery processing in which image formation resumes from a page that has been spoiled by the jam.
Sensors disposed on the conveyance path to detect sheets are used to determine whether there are any remaining sheets in the apparatus at the time of an automatic purge. The sensors cannot detect sheets if the sheets are between the sensors. In this case, the remaining sheets may be falsely recognized as having been all ejected (i.e., the automatic purge is falsely recognized as having been completed), leading to some sheets in the apparatus remaining to be ejected. If image formation resumes in such a state, a newly fed sheet may hit a sheet remaining on the conveyance path and may cause another jam. A high-speed production printing machine, in particular, would be conveying many sheets at the time of a jam, and it is difficult to confirm whether all the sheets have been ejected.
In view of such problems, a sheet conveying apparatus has been proposed which makes an examination sheet, which is fed by a sheet feed tray, travel through the conveying path after the execution of the automatic purge function before the resumption of printing, thereby checking the existence or non-existence of sheets that remain to be removed by the automatic purge (see Japanese Unexamined Patent Application Publication No. 11-180592).
Unfortunately, the above-mentioned prior art obliges users to wastefully consume sheets because it uses an examination sheet to travel through the conveyance path in order to check for abnormalities on the conveyance path. Further, there is a problem of delay in recovery because the apparatus resumes printing after the completion of the ejection of the examination sheet.